1. Technical Field
The present invention relates to a baking-drying water damping paint composition which is a water paint composition into which an inorganic filler is filled to higher extent, and which can form stable and heavy thickness cured paint films by baking.
2. Background Art
Conventionally, sheet-shaped damping members, such as asphalt sheets, have been used in automotive body floors, doors, dashboards, and the like, in order to give them a damping property. Moreover, coating water damping paints, which are adapted for automatically coating with robots and so forth, have been developed recently. However, in the case of ordinary damping paints, since the specific gravity of the resulting paint films is smaller than that of asphalt sheets, it is necessary to further thicken the film thickness, and accordingly there is fear that such problems might arise in that they interfere with the other component parts, form steep irregularities on body floors, and so on. In addition, damping paints are yet highly expensive at present.
As a method to solve the problems, it is possible to think of enhancing the specific gravity of paints by heightening the filling ratio of inorganic fillers into paints, however, when inorganic fillers are filled to higher extent, cracks are likely to occur in the resulting paint films in baking and drying. As a result, there is a problem in that the paint films come off from the substrates to be coated because of the poor adhesion to the substrates to be painted, and it is thus impossible at present to fully effect the performance of paint films with inorganic fillers filled to higher extent.
In Japanese Unexamined Patent Publication (KOKAI) No. 8-209, 056, there is a disclosure on an ordinary-temperature drying water emulsion paint which is good in terms of the adhesion to undercoatings and the damping property. In the paint, 3 kinds of denatured resins, such as (a) a partially cross-linked acrylic resin whose gel ratio is from 10 to 90% by weight, (b) a carboxyl denatured styrene-butadiene rubber and (c) a styrene denatured acrylic resin, are mixed to use them at the same time, and it is considered preferable to compound an inorganic filler in an amount of from 150 to 250 parts with respect to 100 parts of the resinous content.
The paint is an ordinary-temperature drying one, and requires drying at room temperature for 72 hours in order to obtain a paint film whose film thickness is 5000 μm in the examples. When it is baked at higher temperatures in order make the drying faster, it is assumed that a drawback arises in that no normal paint films can be obtained because cracks, swelling and the like occur.
In Japanese Unexamined Patent Publication (KOKAI) No. 9-151,335, a water damping paint is disclosed which includes an inorganic filler in an amount of from 250 to 550 parts by weight and both or either one of a thickening agent and a dispersing agent in an amount from 0.3 to 35 parts by weight with respect to 100 parts by weight of the solid content of a synthetic resin emulsion whose major component is a synthetic resin exhibiting a glass transition temperature of from −50° C. to 5° C. The paint was dried at room temperature in the examples. Nothing is set forth on the gel ratio of the synthetic resin.
In Japanese Unexamined Patent Publication (KOKAI) No. 5-194, 906, there is a disclosure on a composition for water coating, composition which comprises polymer fine particles, dispersed in a water medium, and an inorganic filler. The polymer fine particles are made of two kinds of polymer fine particles, i.e., synthetic rubber emulsion polymer particles whose glass transition temperature is 0° C. or less and emulsion polymer particles whose glass transition temperature is 20° C. or more. Regarding the compounding amount of the inorganic filler into the paint resin, a possibility of such a high compounding amount is disclosed that it can preferably fall in a range of from 120 to 380 parts by weight with respect to 100 parts by weight of the resinous content. However, it is considered appropriate that the thickness of the paint falls in a range of from 200 to 800 μm, and when it is adapted for compositions to be baked at elevated temperatures, it is recommended to carry out 2-stage drying in which it is dried preliminarily at a temperature of from 60 to 100° C. and is thereafter baked at a temperature of from 120 to 160° C.
With the composition for water coating, it is difficult to overcome the drawback that cracks and swelling are likely to occur when paint films, which are applied in a heavy thickness, are baked and dried at high temperatures in one stage. The swelling limit of the paint films obtained in the examples was as thin as from 400 to 1,200 μm, and accordingly it is not possible to obtain heavy thickness paint films which are needed to obtain a damping property.
In Japanese Unexamined Patent Publication (KOKAI) No. 2000-160, 059, there is a disclosure on a water emulsion paint which comprises a water emulsion resin whose gel ratio is from 93 to 97% in an amount of from 20 to 50 parts by weight, and whose a baking temperature is from 70 to 130° C. However, in the paint, since the resin is used which exhibits such a high gel ratio, an inorganic filler is compounded so that calcium carbonate, a filler, is compounded in an amount of 40% by weight at the highest with respect to 30% by weight of the resin as set forth in the examples, and thus the content of the inorganic filler is about 1.3 times the content of the resin at the highest. Since the resinous content exhibits a high gel ratio so that the cross-linking density is enhanced therein, it is impossible to hold the filler in the resin when the inorganic filler is filled in the resin in a double amount or more of the resin, and accordingly cracks, swelling, and the like, occur, and consequently it is difficult to obtain satisfactory paint films.
When inorganic fillers are compounded in baking-drying water paints as described above, in the water paints disclosed conventionally, since there is a fear for cracked paints which are caused by the volumetric contraction of paint films, volumetric contraction which is accompanied by the evaporation of the water content within paints under baking-temperature conditions where the drying of ordinary paint films is carried out, it has been usual practices to dry paints mostly in a low temperature range to make cured paint films, or to decrease the compounding amount of inorganic fillers, or further to simultaneously use special denatured resins in combination. In particular, when inorganic fillers are filled to higher extent in order to reduce costs involved, there is a problem in that the phenomena, such as cracked paint films and swollen paint films, arise remarkably in drying the aforementioned resinous components.
The present invention has been done in view of the aforementioned circumstances, and it is an assignment to propose a baking-drying water damping paint composition, in which an inorganic filler is filled into the resinous component of paints to higher extent, and from which heavy thickness paint films being free from the occurrence of cracks and swelling in baking and drying the paint films can be obtained, in the field of baking-drying water paints.